An occupant protection device for a vehicle includes multiple sensors for detecting collision of the vehicle and a bus line for transmitting a signal of the collision therethrough. JP-A-2007-215102 corresponding to US Patent Application Publication No. 2007/0233919 teaches an air bag device as the occupant protection device. The air bag device includes multiple slave sensors, an air bag ECU, a driver side air bag, a passenger side air bag, a side air bag, a curtain air bag and the like.
The slave sensors are arranged on a right front side, a left front side, a right side near a B pillar, the right side near a C pillar, a left side near the B pillar and the left side near the C pillar in the vehicle. The slave sensors on the right and left front sides detect acceleration in a front-rear direction of the vehicle, and transmit signals via a communication bus line. The slave sensor on the right front side is connected to an air bag ECU via a communication bus line, which is different from a bus line for the slave sensor on the left front side. The slave sensor on the left front side is connected to the air bag ECU via another communication bus line. The slave sensors on the right side near the B pillar and the right side near the C pillar detect acceleration in a right-left direction of the vehicle, and transmit signals via a communication bus line, which is different from a bus line for the slave sensors on the left side near the B pillar and the left side near the C pillar. The slave sensors on the right side near the B pillar and the right side near the C pillar are connected to the air bag ECU via a communication bus line, and the slave sensors on the left side near the B pillar and the left side near the C pillar are connected to the air bag ECU via another communication bus line.
The air bag ECU includes an internal acceleration sensor in the ECU. The ECU determines based on detection results of the slave sensors and the internal acceleration sensor whether the collision occurs. The ECU controls inflation of the driver side air bag, the passenger side air bag, the side air bag and the curtain air bag. Specifically, based on the detection results of the slave sensors on the right and left front sides of the vehicle and the internal acceleration sensor, the ECU controls the inflation of the driver side air bag and the passenger side air bag. Based on the detection results of the slave sensors on the right and left sides near the B pillar and the internal acceleration sensor, the ECU controls the inflation of the side air bag. Based on the detection results of the slave sensors on the right and left sides near the C pillar and the internal acceleration sensor, the ECU controls the inflation of the curtain air bag.
In the air bag device, the air bag ECU is arranged at a position on a front side from a center of the vehicle. Therefore, even when the side of the vehicle near the C pillar collides with an object, the ECU is far apart from the collision portion of the vehicle. Thus, the internal acceleration sensor in the ECU cannot accurately detect the acceleration generated by the collision.
In view of the above difficulty, as shown in FIG. 7, a slave sensor 10 is arranged at a center in the right-left direction of the vehicle near the C pillar. The sensor 10 detects the acceleration in the right-left direction of the vehicle, and the sensor transmits a signal to the air bag ECU 11 via a communication bus line. The ECU 11 controls the inflation of the curtain air bag based on the detection results of the slave sensors 12, 13 near the C pillar and the slave sensor 10 at the center of the vehicle. The sensors 12, 13 on the side of the vehicle near the C pillar function as a main sensor, and the sensor 10 at the center of the vehicle near the C pillar functions as a safing sensor. If the slave sensors 12, 13 and the slave sensor 10 are connected to the ECU 11 via the same communication bus line, the main sensor and the safing sensor are connected to the ECU via the same line. Therefore, when the line is down, the ECU 11 may mistake to detect the collision. Accordingly, as shown in FIG. 7, the sensors 12, 13 near the C pillar are respectively connected to the ECU 11 via the line B1, B2, which is different from the line B3 for the sensor 10 at the center of the vehicle. Thus, the number of the bus lines increases.